The present invention relates to a two-cycle automotive engine with a direct fuel injection system, and more particularly to a system for controlling engine speed to a predetermined speed at an idling state of the engine.
In the two-cycle engine, one cycle of the operation in one cylinder is completed within one revolution of a crankshaft. Accordingly, sufficient amount of air is not drawn in the cylinder.
In a crank-case-scavenged two-stroke engine, a vacuum is produced in an enclosed crankcase of the engine to draw in fresh air when a piston ascends. When the piston descends, burned gas is discharged through an exhaust port while the fresh air in the crankcase is admitted into a cylinder, thereby scavenging the cylinder. On the other hand, a throttle valve is provided in an intake system for the control of engine load. The quantity of intake air is adjusted in accordance with the opening degree of the throttle valve.
However, at light engine load, since the intake air quantity is small, the scavenging becomes insufficient, resulting in misfiring and hence in an irregular engine operation. In addition, a torque characteristic corresponding to the engine operating conditions becomes uneven. Moreover, at heavy engine load, the volume of the crankcase is insufficient for scavenging. Hence, it is desired to increase the scavenging efficiency and prevent fuel from escaping from the cylinder through an exhaust port.
In order to resolve such a problem a two-cycle engine with a separate scavenge pump and a direct fuel injection system is used. Japanese patent application Laid-Open No. 57-203821 discloses a two-cycle engine which is provided with a scavenge pump and a fuel injector. The scavenge pump is provided in a scavenge port and driven at the same speed as the crankshaft to generate a scavenge pressure thereby delivering a sufficient amount of fresh air into the cylinder. The fuel injector is provided in a combustion chamber of the engine for providing a direct fuel injection system so as to prevent the fuel from escaping through the exhaust port.
However, in this disclosed system, control of the load on the engine, in particular in an idling state is not described. In order to control the engine load, a throttle valve may be provided upstream of the scavenge pump for adjusting the quantity of scavenge air. Since the scavenge air quantity is small at the idling state, it is necessary to prevent increase of pumping loss.
Japanese patent application Laid-Open No. 60-501963 discloses a direct fuel injection system in which fuel accumulated in a fuel injector is injected into a cylinder by compressed air. In the system, the air-fuel ratio of the mixture can be effectively controlled in accordance with fuel and air although the quantity of scavenge air is small at idling state.